Golf ball

ABSTRACT

A golf ball has three kinds of dimples A to C on a surface. The A, B and C dimples are circular and have different diameters from each other. In each of the A, B and C dimples, a ratio of the number of dimples to the total number of dimples is 5% or more. The C dimple has a minimum diameter. Moreover, the C dimple also has a maximum depth. In the C dimple, a value of K calculated by the following equation (I) is 0.03 or more:  
       K=de−Di×   0.04    (I)  
     (wherein Di represents a diameter of the specific circular dimple kind and de represents a mean depth of the specific circular dimple kind).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a golf ball and more particularly to an improvement in dimples of the golf ball.

[0003] 2. Description of the Related Art

[0004] A golf ball has approximately 300 to 550 dimples on a surface thereof. The role of the dimples resides in one aspect that such dimples disturb an air stream around the golf ball during the flight of the golf ball to accelerate the transition of a turbulent flow at a boundary layer, thereby causing a turbulent flow separation. The acceleration of the transition of the turbulent flow causes a separating point of air from the golf ball to be shifted backwards so that a pressure resistance is reduced, resulting in an increase in a flight distance of the golf ball. Moreover, the acceleration of the transition of the turbulent flow increases a distance between upper and lower separating points of the golf ball which is caused by a back spin. Consequently, a lift acting on the golf ball is increased.

[0005] A general dimple has a circular shape (a circular plane shape). Examples of an element to greatly influence a flight performance in the circular dimple include a diameter and a depth. In order to enhance an aerodynamic characteristic, various proposals have been made for the diameter and depth of the circular dimple. For example, Japanese Laid-Open Patent Publication No. Sho 62-79072 (1987/79072) has disclosed a golf ball in which two kinds of dimples having different diameters from each other are formed and the ratio of the diameters of both kinds is set to be within a predetermined range. Moreover, Japanese Laid-Open Patent Publication No. Hei 7-155402 (1995/155402) has disclosed a golf ball in which the depths of two kinds of dimples having the same diameter are different from each other.

[0006] In the golf ball, a flight symmetry is one of important evaluation items. In order to realize an excellent flight symmetry, dimples should be evenly present on the surface of the golf ball. For this reason, usually, plural kinds of circular dimples are provided in combination. While the diameter and depth of the circular dimple have been variously improved as described above, the relation of the diameter between dimple types and the relation of the depth between dimple types has rarely been investigated for a conventional golf ball. Usually, a dimple kind having a great diameter has a great depth or the depth is equal for each type. The present inventor has examined that a value of (de−Di×0.04) is −0.02 to 0.02, wherein a diameter is represented by Di and a depth is represented by de in the general circular dimple.

[0007] Although the main role of the dimple has an enhancement in the lift of the golf ball as described above, a golf ball having an excessively great lift provides an insufficient flight distance by the head wind. Moreover, while the flight distance of a golf ball having a comparatively great lift is great in a driver shot, a trajectory tends to be too high in an iron shot so that the flight distance is reduced. To the contrary, in case of a golf ball having a great flight distance in the iron shot, a lift becomes insufficient in the driver shot so that a flight duration becomes insufficient and a flight distance is reduced (so-called drop). Moreover, in case of a golf player having a low head speed, a golf ball having a great lift tends to provide a great flight distance. When such a golf ball is hit by a golf player having a high head speed, a trajectory tends to be excessively high so that the flight distance is reduced. To the contrary, in case of a golf player having a high head speed, a golf ball having a small lift tends to provide a great flight distance. When such a golf ball is hit by a golf player having a low head speed, the flight duration becomes insufficient so that the flight distance is reduced. A golf player is very interested in making a good score and causing the golf ball to fly to a distance. A large number of golf players have desired a golf ball capable of providing a flight distance under any circumstance.

[0008] In consideration of the circumstances, it is an object of the present invention to provide a golf ball having an excellent flight performance.

SUMMARY OF THE INVENTION

[0009] In order to achieve the object, the present invention provides a golf ball comprising, on a surface thereof, a large number of dimples including plural kinds of circular dimples having different diameters from each other,

[0010] wherein when kinds of circular dimples having a ratio of 5% or more to the total number of dimples is set to be specific circular dimple kinds, there are two or more specific circular dimple kinds, and

[0011] when a kind having a minimum diameter in the specific circular dimple kinds is set to be a minimum circular dimple kind, a specific circular dimple kind having a maximum mean depth in all the specific circular dimple kinds is set to be a minimum circular dimple kind.

[0012] In the golf ball, it is possible to obtain a trajectory having a comparatively small height and a sufficient flight duration by the presence of the minimum circular dimple kind in the specific circular dimple kinds which has a maximum mean depth and a minimum diameter. Accordingly, a great flight distance can be obtained irrespective of a wind direction, a used club and a head speed. The reason why such an advantage can be obtained is not clear. However, it can be supposed that a contribution ratio to an enhancement in the lift of the minimum circular dimple kind is low in the first half of a trajectory having a high flight speed (up to the highest point) and a contribution ratio to the enhancement in the lift of the minimum circular dimple kind is high in the second half of a trajectory having a low flight speed.

[0013] It is preferable that a ratio of the number of dimples of the minimum circular dimple kind to the total number of dimples is 10% or more. Consequently, the effect of enhancing a flight distance can be produced remarkably.

[0014] It is preferable that a value of K calculated by an equation (I) in the minimum circular dimple kind is 0.03 or more:

K=de−Di×0.04   (I)

[0015] (wherein Di represents a diameter of the specific circular dimple kind and de represents a mean depth of the specific circular dimple kind).

[0016] Consequently, the effect of enhancing a flight distance can be produced more remarkably.

[0017] It is preferable that the value of K calculated by the equation (I) in the specific circular dimple kinds excluding the minimum circular dimple kind is −0.02 to 0.02. Consequently, a difference between the minimum circular dimple kind and other specific circular dimple kinds becomes clear so that the effect of enhancing a flight distance can be increased by the minimum circular dimple kind.

[0018] It is preferable that the golf ball should have three or more specific circular dimple kinds. Consequently, the dimple effects of enhancing a lift and reducing a drag can be produced still more.

[0019] It is preferable that a ratio of a total dimple area to a surface area of a virtual sphere of the ball is 70% to 90% and a total dimple volume is 250 mm³ to 350 mm³. Consequently, it is possible to obtain a golf ball having a great flight distance.

[0020] The present invention will be described below in detail based on a preferred embodiment with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a plan view showing a golf ball according to an embodiment of the invention,

[0022]FIG. 2 is a front view showing the golf ball in FIG. 1, and

[0023]FIG. 3 is an enlarged sectional view showing a part of the golf ball in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] A golf ball shown in FIGS. 1 and 2 usually has a diameter of approximately 42.67 mm to 43.00 mm. The golf ball has three kinds of dimples A to C on a surface thereof. FIG. 2 shows the dimple kinds (that is, A, B and C) in one compartment obtained by dividing a hemisphere into ten portions. A dimple pattern identical to or symmetrical with a dimple pattern in the compartment is developed over the whole sphere so that a whole dimple pattern can be obtained.

[0025] All of the A, B and C dimples are circular. The number of the A dimples is 70, the number of the B dimples is 210 and the number of the C dimples is 130. Accordingly, the total number of the dimples of the golf ball is 410. The ratio of the number of the A dimples to the total number of the dimples is 17%, the ratio of the number of the B dimples to the total number of the dimples is 51%, and the ratio of the number of the C dimples to the total number of the dimples is 32%. In the present invention, the kind of the circular dimple having a ratio of 5% or more to the total number of the dimples is a specific circular dimple kind. All of the A dimples, the B dimples and the C dimples are the specific circular dimple kinds. The golf ball has three specific circular dimple kinds.

[0026]FIG. 3 is an enlarged sectional view showing a part of the golf ball in FIG. 1. In FIG. 3, the vicinity of the circular dimple is shown. In FIG. 3, points X and Y are boundaries of a virtual spherical surface Sb and a dimple surface Sd in the golf ball. A segment Di connects the points X and Y and is a diameter of a circular dimple. Moreover, a space between the segment Di and the deepest portion of the dimple surface Sd has a depth of de. Moreover, the volume of a region surrounded by a horizontal plane including the segment Di and the dimple surface Sd indicates a dimple volume and the sum of the volumes of all the dimples indicates a total dimple volume. Furthermore, the area of a circle having the diameter Di indicates a dimple area and the sum of dimple areas of all the dimples indicates a total dimple area.

[0027] In the present invention, the specific circular dimple kind having a minimum diameter will be hereinafter referred to as a minimum circular dimple kind. In the golf ball shown in FIGS. 1 and 2, the A dimple has a diameter of 4.1 mm, the B dimple has a diameter of 3.8 mm and the C dimple has a diameter of 3.35 mm. In the golf ball, accordingly, the C dimple has the minimum circular dimple kind. For example, also in the case in which the A dimple is formed in a process for manufacturing a golf ball, the diameter of the dimple has a deviation from 4.1 mm due to a manufacturing error in some cases. In the present invention, the dimple making such a manufacturing error is also set to be the A dimple. Usually, an error may be made within a range of ±0.1 mm with respect to a design value. The depth of each of the A dimples may also make a manufacturing error in some cases. Furthermore, a deep A dimple and a shallow A dimple are arranged in the design stage in some cases. A mean value of the depths of all the A dimples is set to be a mean depth of the A dimple, and so are other specific circular dimple kinds.

[0028] In the golf ball, the mean depth of the C dimple is greater than that of each of the A dimple and the B dimple. Accordingly, a specific circular dimple kind having a maximum mean depth is the minimum circular dimple kind (that is, the C dimple).

[0029] In the golf ball, a trajectory is comparatively low by the presence of the C dimple and can be thereby prevented from being excessively high. In addition, the flight duration is not extremely short. Accordingly, the golf ball can also be prevented from being dropped. In the golf ball, therefore, a flight distance can be prevented from being extremely reduced by the head wind. Moreover, even if the golf ball is hit with any of a wood club such as a driver, a long iron, a middle iron and a short iron, a flight distance can be obtained to some extent. In addition, the golf ball can provide a flight distance to some extent irrespective of the head speed of a golf player.

[0030] In some cases, the mold of the golf ball is provided with a hold pin in order to hold a core and easily carry out releasing. In some cases, moreover, a vent pin is provided for ventilation from a cavity. The tips of the pins are convex in respect of a dimple pattern design, and the mold is constituted such that a dimple can also be formed by the tip of the pin in some cases (the dimple will be hereinafter referred to as a “pin tip dimple”). The pin tip dimple has a specific shape or a very small size in some cases. The number of the pin tip dimples is usually very small, that is, approximately 6 to 14. In some cases, moreover, the small number of minimum dimples are provided in order to reduce a land portion (a portion on the surface of the golf ball other than the dimples) or the small number of maximum dimples are provided in respect of the dimple pattern design in some cases. The kind of the small number of dimples provided on the surface of the golf ball less influence the flight performance of the golf ball. In the present invention, “the ratio of the number of dimples to the total number of dimples is 5% or more” is a requirement for the specific circular dimple kind based on the effect that the number of substantially minimum dimple kinds is defined excluding the small number of dimple kinds.

[0031] The ratio of the number of the dimples of the minimum circular dimple kinds (the C dimple in this example) to the total number of the dimples is preferably 10% or more, and more preferably 15% or more. Consequently, it is possible to further produce the advantage of the minimum circular dimple kind that a trajectory can be reduced and a drop can be suppressed.

[0032] It is preferable that a value of K in the minimum circular dimple kind which is calculated by the equation (I) should be 0.03 or more. A circular dimple having a value of K of 0.03 or more is small and deep. By providing such a minimum circular dimple kind, it is possible to further produce the advantage of the minimum circular dimple kind that the trajectory can be lowered and the drop can be suppressed. If the value of K is too great, the golf ball is formed with difficulty and the dimple is easily clogged with dust. Therefore, the value of K is preferably 0.10 or less, more preferably 0.08 or less, and most preferably 0.05 or less. In order to obtain a golf ball having an excellent flight performance, it is necessary to achieve a proper total dimple volume and a proper surface area occupation ratio as will be described below in detail. In this respect, it is preferable that the values of K in specific circular dimple kinds other than the minimum circular dimple kind should be −0.02 to 0.02.

[0033] It is preferable that the surface area occupation ratio (the ratio of the total area of the dimples to the surface area of the virtual sphere of a ball) should be 70% to 90%. If the surface area occupation ratio is less than 70%, the trajectory becomes too high in a second half. In this respect, it is particularly preferable that the surface area occupation ratio should be 75% or more. It is hard to attain a dimple pattern having a surface area occupation ratio which is more than 90%. In this respect, it is particularly preferable that the surface area occupation ratio should be 85% or less.

[0034] It is preferable that the total dimple volume should be 250 mm³ to 350 mm³. In some cases in which the total dimple volume is less than 250 mm³, the trajectory becomes too high. In this respect, it is particularly preferable that the total dimple volume is 290 mm³ or more. To the contrary, if the total dimple volume is more than 350 mm³, the trajectory might be dropped. In this respect, it is particularly preferable that the total dimple volume should be 330 mm³ or less.

[0035] The diameter of the specific circular dimple kind is usually 2.0 mm to 5.0 mm, preferably 2.2 mm to 4.8 mm, and more preferably 2.4 mm to 4.6 mm. Moreover, the diameter of the minimum circular dimple kind is usually 2.0 mm to 4.0 mm, preferably 2.2 mm to 3.8 mm, and more preferably 2.4 mm to 3.6 mm.

[0036] The mean depth of the specific circular dimple kind is usually 0.05 mm to 0.28 mm, preferably 0.06 mm to 0.26 mm, and more preferably 0.07 mm to 0.24 mm. Moreover, the mean depth of the minimum circular dimple kind is usually 0.10 mm to 0.30 mm, preferably 0.13 mm to 0.28 mm, and more preferably 0.15 mm to 0.25 mm.

[0037] In the present invention, there are two or more specific circular dimple kinds. Since plural kinds of specific circular dimple kinds are present together, an air flow is more disturbed when the golf ball flies. Consequently, it is possible to sufficiently produce dimple effects that a lift can be enhanced and a drag can be reduced. By using plural kinds of specific circular dimple kinds, moreover, the degree of freedom for the design of a dimple pattern can be enhanced. As a result, it is possible to obtain a golf ball which has an excellent even aerodynamic characteristic (a difference in the aerodynamic characteristic is small even if the golf ball is rotated in any direction). In this respect, it is preferable that three or more specific circular dimple kinds should be provided. If the number of the specific circular dimple kinds is too large, the number of the dimples for each specific circular dimple kind is decreased, and furthermore, it is hard to manufacture a mold. From this viewpoint, it is preferable that the number of the specific circular dimple kinds is 20 or less, preferably 10 or less, and more preferably 8 or less.

[0038] While all the dimples formed in the golf ball shown in FIGS. 1 and 2 are circular, the circular dimple and a non-circular dimple may be present together.

[0039] The structure of the golf ball according to the present invention is not particularly restricted. By forming the above-mentioned dimple pattern, it is possible to obtain the effect of enhancing a flight performance in a wound golf ball having a wound core and a solid golf ball (a one-piece golf ball, a two-pieces golf ball and a multi-piece golf ball).

EXAMPLES EXAMPLE 1

[0040] A core formed of a solid rubber was put in a mold and an ionomer resin composition was subjected to injection molding to form a cover around the core. The surface of the cover was coated so that a golf ball according to an example 1 which has a dimple pattern shown in a plan view of FIG. 1 and a front view of FIG. 2 was obtained. An A dimple had a mean depth of 0.1541 mm, a B dimple had a mean depth of 0.1421 mm, and a C dimple had a mean depth of 0.1668 mm. Moreover, a total dimple volume was 300 mm³ and a surface area occupation ratio was 77.7%. Moreover, the golf ball had an outside diameter of approximately 42.70 mm, a weight of approximately 45.4 g and a compression of approximately 90 (by an ATTI compression tester produced by Atti Engineering Co., Ltd.).

EXAMPLE 2 AND COMPARATIVE EXAMPLES 1 AND 2

[0041] Golf balls according to an example 2 and comparative examples 1 and 2 were obtained in the same manner as in the example 1 except that a mold was changed. The dimple patterns of the golf balls are the same as the dimple pattern of the golf ball according to the example 1 and have dimple depths different from the dimple depth according to the example 1. Moreover, a value of K and a total dimple volume are also different from those in the example 1 with a variation in the dimple depth. The dimple depth, the value of K and the total dimple volume are shown in the following Table 1.

Flight Distance Test

[0042] A golf ball according to each of the examples and the comparative examples was launched by the “ULTRA BALL LAUNCHER” produced by Wilson Co., Ltd. and a trajectory, a carry (a distance from a hitting point to a dropping point) and a total flight distance (a distance from the hitting point to a stationary point) were measured. A mean value of results of measurement for 20 golf balls is shown in the following Table 1. The flight distance test was carried out for each of the golf balls on the following three conditions. Condition 1 (target values) A launch speed of a golf ball 73 m/s A launch angle of a golf ball 12 degrees An initial back spin speed 2800 rpm

[0043] The condition 1 is almost equal to the condition on which a golf player having a high head speed hits the golf ball with a driver. Condition 2 (target values) A launch speed of a golf ball 58 m/s A launch angle of a golf ball 12 degrees An initial back spin speed 2800 rpm

[0044] The condition 2 is almost equal to the condition on which a golf player having a low head speed hits the golf ball with a driver. Condition 3 (target values) A launch speed of a golf ball 49 m/s A launch angle of a golf ball 15 degrees An initial back spin speed 4500 rpm

[0045] The condition 3 is almost equal to the condition on which a golf player hits the golf ball with a No. 5 iron. TABLE 1 Result of Flight Distance Test Ex. 1 Ex. 2 Com. Ex. 1 Com. Ex. 2 A dimple Number 70 70 70 70 Diameter (mm) 4.1 4.1 4.1 4.1 Depth (mm) 0.1541 0.1638 0.1651 0.1748 K value −0.01 0.00 0.00 0.01 B dimple Number 210 210 210 210 Diameter (mm) 3.8 3.8 3.8 3.8 Depth (mm) 0.1421 0.1518 0.1531 0.1628 K value −0.01 0.00 0.00 0.01 C dimple Number 130 130 130 130 Diameter (mm) 3.35 3.35 3.35 3.35 Depth (mm) 0.1668 0.1766 0.1351 0.1448 K value 0.03 0.04 0.00 0.01 Total dimple volume (mm³) 300 320 300 320 Surface area occupation 77.7 77.7 77.7 77.7 ratio (%) Condi- Trajectory elevation 14.0 13.8 14.2 13.9 tion 1 angle (deg) Carry (m) 245.6 244.5 242.6 243.6 Total (m) 250.8 249.9 247.3 248.5 Condi- Trajectory elevation 11.9 11.8 12.0 11.8 tion 2 angle (deg) Carry (m) 185.4 184.1 184.4 181.1 Total (m) 207.5 202.7 202.5 199.1 Condi- Trajectory elevation 14.5 14.4 14.8 14.6 tion 3 angle (deg) Carry (m) 150.1 149.0 146.1 149.2 Total (m) 155.2 154.3 151.2 153.8

[0046] In the Table 1, the golf balls according to the examples 1 and 2 have great flight distances on any condition. The golf ball according to the present invention has an excellent flight performance irrespective of a wind direction, a golf player and a used/club. The advantages of the present invention are apparent from the results of evaluation.

[0047] The above description is only illustrative and can be variously changed without departing from the scope of the present invention. 

What is claimed is:
 1. A golf ball comprising, on a surface thereof, a large number of dimples including plural kinds of circular dimples having different diameters from each other, wherein when kinds of circular dimples having a ratio of 5% or more to the total number of dimples is set to be specific circular dimple kinds, there are two or more specific circular dimple kinds, and when a kind having a minimum diameter in the specific circular dimple kinds is set to be a minimum circular dimple kind, a specific circular dimple kind having a maximum mean depth in all the specific circular dimple kinds is set to be a minimum circular dimple kind.
 2. The golf ball according to claim 1, wherein a ratio of the number of dimples of the minimum circular dimple kind to the total number of dimples is 10% or more.
 3. The golf ball according to claim 1, wherein a value of K calculated by an equation (I) in the minimum circular dimple kind is 0.03 or more: K=de−Di×0.04   (I) (wherein Di represents a diameter of the specific circular dimple kind and de represents a mean depth of the specific circular dimple kind).
 4. The golf ball according to claim 3, wherein the value of K calculated by the equation (I) in the specific circular dimple kinds excluding the minimum circular dimple kind is −0.02 to 0.02.
 5. The golf ball according to claim 1, wherein there are three or more specific circular dimple kinds.
 6. The golf ball according to claim 1, wherein a ratio of a total dimple area to a surface area of a virtual sphere of the ball is 70% to 90% and a total dimple volume is 250 mm³ to 350 mm³. 